Most Of Neighborhood Owned By One Person - Should I Buy There?

[Matthew B.]

I have the opportunity to buy a duplex in a neighborhood where 90% of the other properties are owned by the same landlord. Their properties are ok for now, but my concern is that this landlord could get lazy with upkeep/screening or could sell the portfolio to a slumlord and the neighborhood could go downhill quickly. 

Has anyone dealt with this before? Would you buy there?